DESCRIPTION: This proposal addresses several questions about the cytoskeleton in dividing cells and nerve cells and about the cell cycle. Using a variety of methods, including frog eggs and extracts derived from them and nerve cells in tissue culture, these experiments will investigate a wide range of issues. There are six specific aims. In aim 1, a factor from Xenopus embryo extracts that increases the depolymerization of microtubules will be purified and its gene cloned and characterized. In aim 2 the role of the actin cytoskeleton in the surface contraction waves seen in Xenopus eggs will be examined. In aim 3 mechanisms of microtubule transport will be examined in culture hippocampal neuron axons and dendrites. In aim 4 the interaction between actin and the microtubule cytoskeleton will be investigated in neuronal growth cones. In aim 5 the regulation of G1 cyclins will be examined, particularly defining the targets of cyclin E/cdk2 needed for the activation of DNA replication. In aim 6 the activation of cdc2 by cyclin B and the identity and role of other activators and inhibitors will be studied.